Screwgate is below standards for a production/work climber but there are no rules for rec climbers. Many rec climbers use screwgates. I would be consistent in what ever gate technology I used for life support use and a redirect is life support. So if you use a screwgate to anchor your rope on your harness then use it for your redirects. If you use autolockers on your harness and lanyards do the same for redirects. Otherwise you're setting yourself up for a mistake when you're tired, stressed or lacking concentration. Be consistent, don't make your brain do flip flops around life support connections.

The way I see it, if you're trying to figure out a way to make screwgates more secure then you probably shouldn't be climbing on them.
-moss